Sludge dewatering in a conventional plant with phosphorus removal-I: Analysis of additional costs

The aim of this research is to assess the differences in quantity and quality of sludges produced in a conventional activated sludge plant, modified for phosphorus chemical removal. Tests were carried out at the Cesenatico sewage treatment plant, where in summer phosphorus is removed simultaneously to the biological process with the aid of aluminium or ferrous sulphate. Characteristics of the sludge produced with or without phosphorus removal were compared. The sludge was then dewatered by a centrifuge and a filter-press on pilot scale and many tests were carried out under different operating conditions.In this part, the plant's most important performances are discussed with regard to phosphorus removal efficiency, sludge production, characteristics and dewaterability. The experiments showed that phosphorus could be removed up to residual concentration of 1.6 mg 1^?1 without detrimental effects on the biological process, with an increase of sludge production of 21 and 36% using aluminium or ferrous sulphate respectively. On the basis of experimental results a costs analysis was carried out to assess the costs for phosphorus removal, including the additional ones for sludge conditioning, dewatering and cake transport to landfill. It results that additional costs vary from 3290 to 6380 Lit per capita per year (29–54%). The higher costs refer to smaller plants (50,000 inhabitants), in which aluminium sulphate is used and sludge dewatered by centrifuge. The use of ferrous rather than aluminium sulphate allows savings of 1300–1600 Lit per capita per year.     

The thickening and treatment of sewage sludges to minimize phosphorus release

The Johannesburg City Council has operated biological and chemical nutrient removal wastewater treatment plants for the past 15–16 years. With the advent of more sophisticated sludge handling techniques, problems have been experienced with the recycle of phosphorus-rich sludge processing liquors to the liquid phase. These problems are expected to increase in the future. This paper describes laboratory and pilot scale experiments to determine viable methods for phosphorus removal from sludge liquors and ways of obviating phosphorus release from phosphorus-rich activated sludges. The design of new full-scale plants being constructed to pretreat phosphorus-rich sludges prior to dewatering are also discussed. The paper also describes innovative process layouts for sludge treatment keeping in mind various options for final sludge disposal. Emphasis is placed on the pre-aeration and phosphate precipitation from anaerobically digested and raw primary sludges and techniques for the thickening and dewatering of primary and waste activated sludges to minimize phosphate release into the liquors so produced. The technique of sludge thickening on linear screens is described and the coupling of linear screens to belt presses to complete the dewatering operation.     

The balance of heavy metals through a sewage treatment works I. Lead,cadmium and copper

Concentrations of lead, cadmium and copper have been determined in the sewage sludges, sewages and effluent of a sewage treatment works. Treatment at this works is by primary sedimentation prior to biological treatment in a diffused air activated sludge plant. By analysis of composite samples corresponding to a 24-h input of raw sewage to the works, a mass balance of metals through the works has been estimated. The partition of the metals from raw sewage into the settled sewage and primary sludge, and from the settled sewage into the activated sludge and final effluent has been quantified.     

The balance of heavy metals through a sewage treatment works II. Chromium,nickel and zinc

Concentrations of chromium, nickel and zinc have been determined in the sewage sludges, sewages and effluent of a sewage-treatment works. Treatment at this works is by primary sedimentation prior to biological treatment in a diffused air activated sludge plant. By analysis of composite samples corresponding to a 24-h input of raw sewage to the works, a mass balance of these metals through the works has been estimated. The partition of these metals from raw sewage into settled sewage and primary sludge, and from the settled sewage into the activated sludge and final effluent has been quantified.     

Fate of natural estrogens in batch mixing experiments using municipal sewage and activated sludge

Since natural estrogens such as 17beta-estradiol (E2) and estrone (E1) are excreted daily by humans, E2 and E1, which are classified as inevitable endocrine-disrupting chemicals, are always present in sewage wastewater. For several years, the monitoring and removal of natural estrogens at sewage treatment plants have been examined by many investigators. However, little is known regarding the exact behavior of estrogens in actual sewage when in contact with activated sludge. In this study, the fate of E2 and E1 as a result of adsorption and decomposition in batch mixing experiments using municipal wastewater and activated sludge collected from an actual municipal sewage treatment plant was investigated. Estrogen concentrations were determined using an enzyme-linked immunosorbent assay (ELISA) kit. E2 and E1 in sewage were removed from the liquid phase in contact with activated sludge, and E2 and E1 adsorbed on the sludge were decomposed in 4h. Significant changes in the adsorption and decomposition of E2 and E1 on the sludge were not observed at low temperatures or when different sludge samples were used such as those acclimatized to low-loading and high-loading conditions. In contrast, the processes leading to the removal of estrogens, such as the adsorption and decomposition of estrogens in contact with activated sludge, were inactivated by sterilizing the sludge. Natural estrogens adsorb onto the activated sludge, and are therefore easy to be biodegraded. In a biological reaction process, therefore, the estrogens will be rapidly removed at the initial stage, when the sewage is satisfactorily mixed with the sludge.     

Behaviour of persistent organochlorine micropollutants during primary sedimentation of waste water

The removal of polychlorinated biphenyls and the organochlorine insecticides gamma-HCH, aldrin, dieldrin and endrin during primary sedimentation of raw sewage has been studied using a pilot plant facility. A matrix of sixteen experiments was performed, where the pilot plant was operated at four different hydraulic loadings with four different influent suspended solids loadings. Significant removals of micropollutants into the primary sludge were observed, although no particular relationship with the removal of suspended solids was evident. It is concluded that a proportion of the organic microcontaminants present in raw sewage were associated with non-settleable solids and were also in the dissolved form. The significance of the behaviour of organochlorine micropollutants in waste water treatment processes and the hydrological cycle are discussed in the context of water re-use operations.     

Removal of zeolite type a during primary sedimentation and its effect on metal removal

Using two pilot plants operated in parallel, treating settled sewage the removal of the detergent builder zeolite type A during primary sedimentation has been studied. With one zeolite free pilot plant acting as a control to the other it was also possible to determine the effect of zeolite on suspended solids and heavy metal removal over a range of hydraulic loadings. At both influent concentrations of zeolite studied (30 and 60 mg l⁻¹) zeolite removal was substantial under all conditions. No evidence of enhanced removal of suspended solids in the presence of zeolite was observed. Removals of lead, zinc, copper and chromium were slightly enhanced in some experiments. The observed improvements in metal removal appeared to be strongly influenced by the sewage matrix.     

腐殖活性污泥工艺在日本和韩国的应用

腐殖活性污泥工艺是在传统活性污泥工艺的基础上增加了填充腐殖土填料的生物培养装置，用于改善活性污泥特性，提高处理效果的新型污水处理方法。自20世纪80年代起，日本已成功地将该工艺应用于岛内住宅小区污水净化站、山之内水质净化中心、乌栖市饭田地区和永吉地区农田排水处理站等多个污水处理厂，在韩国也已有200多个污水处理厂应用了该技术。运行结果表明，该工艺具有脱氮除磷效果好、污泥产量低、污泥脱水性好和污泥不产生臭气等显著优点。     

盐度对膜生物反应器去除污染物效果的影响

含盐污水经市政管网进入污水厂后可能会对生物处理系统产生影响。为此采用膜生物反应器(MBR)处理不同盐度的污水,考察了各盐度下的除污效果。当进水盐度分别为1%(即含盐量为10 g/L)、2%、3%和4%时,对CODMn的平均去除率分别为85.2%、81.8%、76.0%、73.7%;对氨氮的平均去除率分别为90.6%、88.4%、86.8%、79.5%;对总氮的平均去除率分别为41.1%、37.4%、35.8%、33.1%。同一盐度下,对CODMn、氨氮和总氮等污染物的去除率都是先下降后升高,最后趋于平稳。但从总体来看,随着盐度的升高,对各污染物的去除率和污泥浓度均呈下降趋势。含盐环境下微生物所分泌的大量胞外聚合物是造成膜污染的主要原因。     

The influence of heat treatment on the metallic and polycyclic aromatic hydrocarbon content of sewage sludge: A pilot plant study

Heat treatment of sewage sludge facilitates its dewatering. The liquors produced inevitably contain a portion of the heavy metal and polycyclic aromatic hydrocarbon contaminants present in the sludges. Using a pilot plant, the influence of time and temperature of treatment on the concentrations of these pollutants in the liquors and treated sludges from three types of untreated sludge have been determined. Statistical analysis of the data has been used to identify significant effects of the treatment process. It is concluded that heat treatment would not produce significant increases in the concentrations of these contaminants in sewage effluents.     

剩余污泥回流至初沉池对A/O污水处理系统的影响

基于静态模拟试验结果，进行了将A／O处理工艺中二沉池剩余污泥按比例回流至初沉池的生产性试验，运行结果显示，这一措施能明显提高初沉池的沉淀效率，且当剩余污泥的回流比例为40％～60％时，初沉池对SS、COD等去除效果最佳，同时可提高A／O池进水的可生化性及处理能力，并降低浓缩池出泥含水率。该工艺运行稳定，可有效降低污水处理厂的总体运行成本。     

浅谈重金属对污水处理中活性污泥影响

综述了污水处理中重金属对生物反应动力学常数,活性污泥微生物群落结构及污水生物处理效率的影响,进而研究了重金属对生物脱氮除磷的毒性效应,对提高污水处理效果具有重要的现实意义。     

Assessment of virus removal by a multi-stage activated sludge process

Viruses seeded into a 50,000 gal day⁻¹ three-stage activated sludge pilot plant were effectively reduced in the treatment process. Reduction was highest in the system's denitrification and high-rate activated sludge modules, both averaging more than 95% virus removal. Combining the removal capacity of each unit process resulted in a calculated virus reduction of 99.97% for the total treatment system.A study of the indigenous viruses present after primary settling illustrated the wide diversions that can occur in wastewaters during a 24 h period. It illustrated as well the necessity of collecting temporally related samples within the treatment system. No direct relationship was evident between the numbers of coliphages and enteroviruses present in the primary effluent.     

Control of activated sludge settleability using preaeration and preprecipitation

This paper deals with the addition of a preaeration and a preprecipitation stage to a conventional activated sludge process. The experiments were carried out in a pilot plant using wastewater from the city of Valencia (Spain) as feed. The effect of the F/M ratio and sludge age on sludge settleability was established. In both cases, process stability was observed to increase with respect to the conventional process. Good sludge settleability was thus assured in a greater F/M ratio range. A comparative economic study was also carried out.     

Removal of indigenous rotaviruses during primary settling and activated-sludge treatment of raw sewage

An eight month study of indigenous rotavirus removal during primary settling and activated sludge treatment of raw sewage was made in a plant in Houston, Texas treating 1.5 million gal day⁻¹. An average reduction of 44–55% was obtained by primary settling and a 93–99% reduction was achieved in final chlorinated effluents. Composite sampling at 1 h intervals over a 24 h period indicated average removals of 85% compared to a misleading 6% indicated by one set of grab samples of raw sewage and effluent collected simultaneously. Quantification of rotaviruses was made by immunofluorescent foci counts 24 h after addition of sample concentrates to coverslip cultures of fetal rhesus kidney cells. Rotaviruses varied from 40–5101⁻¹ of raw sewage and from 0 to 25 in the final chlorinated effluent.     

腐殖土强化活性污泥工艺的除污效果研究

分别采用腐殖土强化活性污泥系统与普通活性污泥系统处理生活污水,考察了对COD、NH3-N、TN、TP的去除效果.结果表明,腐殖土强化活性污泥系统与普通活性污泥系统对有机物的去除效果差别不大,平均去除率都在86%左右;腐殖土可以强化普通活性污泥系统对营养盐的去除,特别是明显提高了TP的去除效果,腐殖土强化活性污泥系统对NH3-N、TN和TP的平均去除率分别为71.50%、54,83%和62.67%,比普通活性污泥系统分别高出8.67%、8.16%和33.84%.可见,增加腐殖土反应器是改善普通活性污泥系统脱氮除磷效果的有效方法.     

The effects of organotin on the activated sludge process

Organotin compounds which find increasing use in marine antifouling paints may be present in the discharge from dry dock operations. This investigation was aimed at determining the effect of such wastewater when discharged to a municipal activated sludge treatment plant. Experiments were conducted using a Warburg respirometer and continuous flow bench-scale activated sludge systems. The results showed that unacclimated biological cultures can be inhibited by tributyl tin oxide (TBTO^™) concentrations as low as 25 μgl⁻¹. However, TBTO doses of over 8000 μgl⁻¹ can be tolerated by a well acclimated culture. Continuous loading of up to 1000 μgl⁻¹ TBTO had no effect on organic removal in activated sludge systems. However, an adverse effect on sludge settleability was noticed at 100 μgl⁻¹ TBTO. Shock loadings of 500 and 1000 μgl⁻¹ TBTO had no effect on soluble organic removal but resulted in impaired settling and higher effluent suspended solids. The LC₅₀ of TBTO to the fathead minnow was estimated at 45–200 μgl⁻¹. The toxicity was reduced considerably by activated sludge treatment.     

Re-use of water treatment works sludge to enhance particulate pollutant removal from sewage

This paper attempted to study the feasibility of reusing water treatment works sludge ("alum sludge") to improve particulate pollutant removal from sewage. The main issues focused upon were: (1) the appropriate dosage of the alum sludge, (2) the appropriate operating conditions, and (3) the possible mechanisms for enhancement by adding alum sludge. Actual alum sludge and sewage were applied to a series of jar tests conducted under various conditions. It has been found that both the SS and COD removal efficiencies could be improved by the addition of the alum sludge, which was mainly attributed to the removal of relatively fine particles with a size of 48-200 microm. The appropriate dosage of the alum sludge was determined to be 18-20 mg of Al/L. Increasing the mixing speed or reducing the floc size of the alum sludge enhanced the SS and COD removal and the dispersed alum sludge could remove particulate contaminants with smaller size than the raw sewage. ToF-SIMS evidence revealed that the aluminum species at the surface of the alum sludge were effectively utilized for improving the SS and COD removal. It was postulated that the sweep flocculation and/or the physical adsorption might play key roles in the enhancement of particulate pollutant removal from sewage.     

污泥浓缩脱水一体化技术应用探讨

传统的污泥浓缩脱水工艺存在着占地大、投资多、管理复杂、污泥容易流失、除磷效果差的缺陷,严重地影响看污水处理厂建设的良性发展。提出了污泥浓缩脱水一体化技术在污水处理厂中的应用,并就其基本原理和技术特点进行了阐述。为污水处理厂污染工艺选择提供了一种新的思路。对加快污水处理厂建设,提高出水标准,保护环境起到积极的作用。     

预氧化联合污泥回流处理低浊微污染水试验研究

研究了采用高锰酸钾预氧化与污泥回流联用工艺对低浊微污染原水的处理效果。结果表明,采用污泥回流可有效改善沉后水浊度,最佳回流比为60%,沉后水浊度从无回流时的1.91NTU下降到1.51NTU;粉末活性炭与污泥一同回流能改善滤后水有机物的去除效果。投加高锰酸钾进一步提高了处理效果,污泥回流则强化了高锰酸钾的助凝除浊效果,使有机物去除作用更显著。